Hello,
You've picked what I consider to be amongst the hardest campaigns, especially the first 2 missions in BoB Crisis.
The rank you select will determine where you sit in the formation; highest rank and you'll lead. The mission briefing page will tell you which. Usually you'll be the wingman to the leader, so once you start engine, go to external view and follow the first plane to move; that's your leader.
The plane markings normally determine who the leader is, but if you're playing this in 'Red Core', all BoB campaigns now start with a/c markings turned off for some reason.
Don't get into a melee. What I find in missions with large numbers of a/c is, a lot of enemy ai single out the player and shoot the crap out of you from every angle. For me it's still the most annoying aspect of this game. In a dozen or so attempts at that first mission over the years, I reckon I've come away unscathed probably twice. keep your speed and altitude up, fly through the enemy formation on your first pass and get into a safe position before attempting another intercept; in other words, choose your moments. Don't just have a go at any enemy plane in range.
Personally, I just delete campaigns where I end up getting chased by just about every ai plane as though you're the only enemy in the sky, especially when you gotta fly for 40 mins or more just to see any action. Even when using the skip function you end up looking at a black screen for what seems like 3 days. Sometimes I reckon I could go out and buy a burger, take a dump and still find myself waiting....only to get the crap shot out of you by 9 spitfires in the first 10 seconds of combat....then I ask myself, 'Do I really want to go through all that again in hope of getting a better result??!!' The answer is usually, 'No, I have better things to do with my time'.